DESCRIPTION: Schwannomas are benign tumors of the peripheral nervous system which commonly occur in their solitary form in otherwise normal individuals. Rarely, individuals develop multiple schwannomas arising from one or many elements of the peripheral nervous system, either associated with the classic tumor suppressor gene syndrome neurofibromatosis 2 (NF2) or without vestibular nerve involvement (schwannomatosis). The hypothesis of this study is that schwannomatosis is a distinct clinical entity caused by genetic inactivation of a tumor suppressor gene. The steps proposed to investigate this hypothesis are: 1. Clinical characterization of a cohort of patients with schwannomatosis and related syndromes. 2. Molecular genetic analysis of the NF2 gene in tumorous and non tumorous tissues from these patients. 3. Microsatellite analysis to identify other possible loci for this syndrome. The goals of this project include a further understanding of the functioning of the NF2 tumor suppressor gene and the identification of other genes which may be involved in schwannoma formation. This information will not only be helpful to the understanding of NF2 and related disorders, but will also contribute to the rapidly expanding field of genetic causes of tumor formation, including the recognition of the role of atypical genetics such as somatic instability and mosaicism. This research plan will lay the framework for the establishment of schwannomatosis as a third major form of NF and lead to both improved clinical recognition and management and greater scientific understanding of the processes leading to NF.